The faster lens would be nice, but especially for Canon users, the full 180 degree image of the 10-17 (at 10mm) may be more attractive than the 167 degrees of this Sigma. The full 180 is only for the Nikon sensor it seems.

Also nice, though, for those wanting to use a Magic Filter is there is a rear filter holder.

This is bad news. I thought Sigma must have something in the works to fill the Canon FE gap and was pleased to see that they _Finally_ had done it. Not even close and definately no cigar.

The shame of it is that Nikon already has a great WA Fisheye option, only Canon does not. So to whom do they expect this lens to appeal to? I think they missed their biggest potential market.

Now the new 4.5mm seems to me to be much more exciting. I think true circular shots do have their place for artistic shots, and the otherworldly views underwater lend themselves to this. For those looking for something to distinguish some of their shots this is the lens. Now APCS usesrs can join in the fun too. Just don't overdo it.

I might get one of these myself. But this lens is even more specialize than a full frame fisheye and would really be the kind of kit I'd rather borrow for a few special dives than one to own. Maybe we could create a Wetpixel cooperative?

The Tokina is a great lens and a good option for Canon shooters to get a full-frame fisheye. But its a completely different lens if you ask me. Its in a class by itself really, its an ultrawide (weitwinkel) zoom and a 15mm FE and a 10.5mm fisheye in one. It does what a 10mm prime can do but its not without its drawbacks. Image quality is good but not as good as a prime lens and its not a f2.8.

So there still is a bit of a gap for Canon cropped sensor users. Sigma could have filled it--but didn't.

Given the choice I would rather have the full 180 degree coverage and sacrifice a little on image quality and stick with the Tokina. I don't really see any motivation for Canon users to buy the Sigma.

For Nikon its a much harder choice. There are advantages to a prime lens over the zoom and advantages to the zoom over the prime. There is almost room for both lenses in the bag. But Sigma is pretty much a moot point since we already have a good choice in the Nikon 10.5. Only if CA and price are much better could the Sigma be competative. But even then its a small market and always a hard sell for the 3rd party lenses.

Thanks for the correction Matt.
Clearly there must be more going on here than the diffference in crop factor between Nikon and Canon. What is it about the cropped digital design for Canon that makes full 108 degree FOV so difficult?

Sure 167 degrees is still wide, but its too bad that even now there is no 180 degree solution for Canon. So I guess the Sigma will have a market after all.....unfortunately

I don't believe it's necessarily more difficult to design a 180deg FOV for the Canon - only a decision by the manufacturers to maximize compatibility (and profit ).

The Nikon 1.5x-crop sensor is ever-so-slightly larger than the Canon 1.6x crop - if lens manufacturers made a 180deg coverage lens specifically for the Canon sensor (smaller image circle), it would have >180deg FOV and/or exhibit severe vignetting on the Nikon. End result: no Nikon buyers.

It's understandable, if unfortunate for Canon users, that they design to Nikon sizing.

These are fisheye lenses. A difference of 13 degrees diagonally probably only translates into 1 or 2 degrees horizontally and vertically next to no difference. I would be very surprized if anyone noticed the difference in real life.

Also, as matt pointed out, as evidence of this, the same thing was true with the Tokina 10-17, and I've never heard anyone complaining that they were dissapointed in the angle of view they got from that lens.....

The big diffference that Sigma made was pointing out the fact that there was a difference, as if they had not pointed it out themselves it would not be an issue.